UPDATE 1-S&P cuts $22 bln subprime RMBS, affirms $531.6 bln

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NEW YORK, Oct 19 (Reuters) - Standard & Poor's on Friday cut ratings on about $22.02 billion of U.S. residential mortgage-backed securities backed by subprime loans, citing increased delinquencies and foreclosures.

The downgrades affected 1,413 classes of RMBS issued between the fourth quarter of 2005 and fourth quarter of 2006, S&P said in a statement.

Delinquencies on the classes downgraded averaged 23.3 percent, S&P said. The RMBS classes were backed by first-lien subprime loans from 325 transactions, S&P said.

"Standard & Poor's expects that conditions in the U.S. housing market, especially in the subprime sector, will continue to decline before they improve, with home prices remaining under stress," the rating agency said.

Ratings on $531.6 billion of RMBS issued during this period were affirmed, S&P said.

Ratings of asset-backed commercial paper conduits with exposure to the downgraded RMBS classes are not affected, S&P said.